Mapping ionized gas properties in NGC 4258 with SITELLE: A laboratory to study the connection between AGN and Star Formation

Abstract

In this study, we present Integral Field Spectroscopy (IFS) observations of NGC 4258, a spiral galaxy hosting a Low-Luminosity Active Galactic Nucleus (AGN) and a collimated jet. These observations were conducted using the Spectro-Imageur à Transformée de Fourier pour l’Étude en Long et en Large des raies d’Émission (SITELLE) instrument at the Canada-France-Hawaii Telescope of emission-line fluxes for [OII]$\lambda$3727, H$\beta$, [OIII]$\lambda\lambda$4959,5007, [NII]$\lambda$6548, H$\alpha$, [NII]$\lambda$6583, [SII]$\lambda\lambda$6716,31, analysed the spatial distribution, and explored the properties of the ionized gas in the interstellar medium (ISM) and the diagnostic BPT diagrams. The results show that higher excitation gas is preferentially located in the galaxy’s centre, consistent with the AGN activity, followed by the LINERS and Composite region located mainly along the jet. The inner and outer spiral arms exhibit star-forming regions showing evidence of shocks well-reproduced by fast shock photoionization models. The emission from the jet is consistent with both the AGN activity and shocks being the ionization source, reaching velocity dispersions up to 250 $\text{km}$ $\text{s}^{-1}$ in H$\alpha$ at a distance of up to 6 kpc from the nucleus toward the bifurcations seen in the south-east jet. By using the mixing sequence defined in the BPT diagrams and correcting H$\alpha$ emission for dust extinction, we derived a galaxy-wide star formation rate of 3 $\text{M}_\odot$ $\text{yr}^{-1}$ and a value of 0.3 $\text{M}_\odot$ $\text{yr}^{-1}$ for the central 3.4 $\text{kpc}^2$.

Ray Garner

TAMU Astronomy Postdoctoral Researcher

I’m a scientist, Star Wars fan, and amateur photographer raised in Georgia. My research interests include galaxy evolution, star formation, satellite galaxies, and nebular diagnostics.